Restrict transformation to Header row or Row 1 Power Query - excel

Question

I need to find and replace the headers of my Source Table in Power query
I am able to do this with BulkReplace
But this searches the entire table, is there a way to restrict BulkReplace to only the headers, or if not then I can demote the headers and run BulkReplace on just Row 1 of the Source Table
Thank you
sumAppHeads (Find Replace Table)
In my Power Query, I have
BulkReplaceStepHeaders = fBulkReplaceStep(#"Demoted Headers", sumAppHeaders, Table.ColumnNames(#"Demoted Headers")),
let BulkReplace = (DataTable as table, FindReplaceTable as table, DataTableColumn as list) =>
let
//Convert the FindReplaceTable to a list using the Table.ToRows function
//so we can reference the list with an index number
FindReplaceList = Table.ToRows(FindReplaceTable),
//Count number of rows in the FindReplaceTable to determine
//how many iterations are needed
Counter = Table.RowCount(FindReplaceTable),
//Define a function to iterate over our list
//with the Table.ReplaceValue function
BulkReplaceValues = (DataTableTemp, n) =>
let
//Replace values using nth item in FindReplaceList
ReplaceTable = Table.ReplaceValue(
DataTableTemp,
//replace null with empty string in nth item
if FindReplaceList{n}{0} = null then "" else FindReplaceList{n}{0},
if FindReplaceList{n}{1} = null then "" else FindReplaceList{n}{1},
Replacer.ReplaceValue,
DataTableColumn
)
in
//if we are not at the end of the FindReplaceList
//then iterate through Table.ReplaceValue again
if n = Counter - 1
then ReplaceTable
else #BulkReplaceValues(ReplaceTable, n + 1),
//Evaluate the sub-function at the first row
Output = BulkReplaceValues(DataTable, 0)
in
Output
in
BulkReplace

Answer 1

Demote the headers
Transpose the table
Replace the old column names that are now all in Column1
Transpose the table back
Promote the headers

Answer 2

Try this
BulkReplaceStepHeaders = fBulkReplaceStep(Table.FirstN(#"Demoted Headers", 1),sumAppHeaders,Table.ColumnNames(#"Demoted Headers")) & Table.Skip(#"Demoted Headers", 1),

Answer 3

This grabs the column names, merges against the replace table to find new names, then does a rename to use the new names
let Source = Excel.CurrentWorkbook(){[Name="Table1"]}[Content],
#"Merged Queries" = Table.NestedJoin(Table.FromList(Table.ColumnNames(Source)), {"Column1"}, ReplaceTable, {"Find"}, "Table2", JoinKind.LeftOuter),
#"Expanded Table2" = Table.ExpandTableColumn(#"Merged Queries", "Table2", {"Replace"}, {"Replace"}),
#"NewNames" = Table.AddColumn(#"Expanded Table2", "Custom", each if [Replace]=null then [Column1] else [Replace])[Custom],
#"Rename"=Table.RenameColumns( Source, List.Zip( { Table.ColumnNames( Source ), #"NewNames" } ) )
in #"Rename"